1. Field of the Invention
The present invention relates to substrate for growing a wurtzite-type crystal comprising a laminated structure a first layer of which includes a crystal with six-fold symmetry, which wurtzite-type crystal exemplifies, and a second layer of which includes a metal oxynitride crystal, and a method for manufacturing the same, and a semiconductor device.
2. Description of the Related Art
In recent years, attention has been paid to a light receiving and emitting element using an InGaN-based semiconductor because it is considered that when an InGaN nitride semiconductor is used as a light receiving and emitting element, light can be received and emitted in a very wide band, from the ultraviolet region to the infrared region because the optical band gap of InN is 0.7 eV (in the infrared region), and the optical band gap of GaN is 3.4 eV (in the ultraviolet region). Also, because of the small electron effective mass, high-frequency operation can be expected, also, when application to an electronic device is considered. From the above background, research and development on InGaN have become active in recent years. These related techniques are described in, for example, Japanese Patent No. 2751963, Applied Physics Letters Vol. 92, p. 262110 (2008), Physica Status Solidi (c) 5, No. 1, p. 143 (2008), and Proceedings of SPIE, Vol. 6669, p. 66690X (2007).
However, there is a problem that no crystal substrate lattice-matched with InGaN, which is a wurtzite-type crystal, exists. A method in which, as in GaN, sapphire (Al2O3) is used as a substrate, and InGaN is directly grown on sapphire is used, but the crystallinity of the obtained film is low. Therefore, Japanese Patent No. 2751963 and Applied Physics Letters Vol. 92, p. 262110 (2008) and Physica Status Solidi (c) 5, No. 1, p. 143 (2008), propose a method in which first, a GaN layer is grown on sapphire, and then, InGaN growth is performed. In the above method, InGaN is grown after the GaN layer is grown, and therefore, there is an advantage that the formation of a rotation domain in the growth plane is suppressed, so that high crystallinity is obtained.
However, the a-axis lattice constant of GaN and InN is 0.3189 nm and 0.3548 nm respectively and since these values are quite different, any high-quality InGaN obtained so far is only of a Ga-rich composition. Various factors can be considered for this, and one factor is that when InGaN is grown on GaN, due to a Ga composition drawing-in effect (an effect that In atoms are not easily taken in to decrease the lattice mismatch with the GaN substrate layer) at the early stage of growth, it is difficult to obtain a crystal having a lattice constant largely different from that of the substrate layer.
Therefore, in Proceedings of SPIE Vol. 6669, p. 66690X (2007), an attempt to form InGaN on a ZnO substrate is made because ZnO has a larger lattice constant than GaN, and a small lattice mismatch with InGaN. But, the composition of In completely lattice-matched with ZnO is In/(In+Ga)=18 atomic %, and it is still difficult to form an In-rich, high-quality InGaN film.
The present invention solves the above problems, and it is an object of the present invention to provide a substrate for growing a wurtzite-type crystal comprising a laminated structure having the desired lattice constant and excellent crystallinity, and a method for manufacturing the same. Also, it is another object of the present invention to provide a semiconductor device using the above substrate for growing a wurtzite-type crystal comprising a laminated structure.